1. Field of the Invention
The invention relates to elements composed of insulating glazed elements composed of at least two glass sheets separated from each other by a small space in which a vacuum has been created.
2. Description of the Related Art
In order to obtain thermal and acoustic insulation, it is usual to produce insulating glazing assemblies comprising two glass sheets separated from each other by a relatively large air cavity. Such glazing assemblies provide thermal insulation which is regarded as unsatisfactory for certain applications. To remedy this, it is known to produce glazing assemblies comprising three glass sheets, it being possible for one of the air cavities to be replaced with a gas, for example krypton. These glazing assemblies have markedly improved thermal insulation properties but have such a thickness that it is not always easy to use them. Moreover, users are currently demanding the thermal insulation properties of glazing assemblies to be equivalent to that of solid partitions, i.e., walls.
Insulating glazing assemblies have already been proposed, especially in EP-A-0,645,516, which consist of two glass sheets separated from each other by a small space in which a vacuum has been created. The glass sheets are separated from each other by mounts distributed over their entire surfaces, the sheets being joined together around their periphery by an inorganic seal.
Because of the vacuum, these glazing assemblies provide very good insulation, but because of this very good insulation they may rapidly be covered with condensation, or even frost, for example when there is a rapid increase in the temperature of the ambient air. This is because there is no heat transfer between the two glass sheets constituting the glazing assembly due to the vacuum created between the two glass sheets. Each glass sheet is therefore at the temperature of the ambient air towards which it faces and their respective temperatures do not affect each other, unlike in the usual insulating glazing assemblies. Upon a rapid increase in the temperature of the ambient air, that face of the glazing assembly oriented towards the ambient air does not heat up rapidly and may thus be at a temperature below the temperature of the dew point of this ambient air, hence the appearance of condensation, or even of frost if the temperature of the glass sheet is very low. A rapid increase in the temperature of the ambient air should be understood to mean an increase in temperatures whose rate of change is substantially greater than the consequent rate of change of the temperature of the glass sheet in contact with this ambient air.
Thus, despite their very good insulation, these types of insulating glazing assemblies lose their primary function in certain applications such as, for example, a door of a refrigerating enclosure after the door has been opened. That is to say they no longer fulfil their function of providing visibility through the wall because of this temporary loss of transparency.